Little is known of the biochemical nature or genetic origins of the individually distinct transplantation antigens which characterize chemically induced sarcomas of inbred mice. Serological reagents detecting these antigens would clearly facilitate their analysis. We have successfully defined two serologically distinct cell surface antigens of methylcholanthrene-induced sarcomas of BALB/c origin, Meth A and CMS4. The exceedingly limited tumor distribution of these antigens resembles in this respect the individually distinct transplantation antigens of these tumors. We now plan to apply hybridoma methodology to this analysis. Monoclonal antibody will be screened for reactivity to cell surface antigens using several serological assays and a panel of normal and transformed cell types. The initial aim of our analysis will be to classify the range of cell surface antigens being identified. Our second aim will be to obtain a molecular characterization of transformation-related and individually distinct antigens. This will involve one- and two-dimensional SDS-PAGE and peptide analysis of proteins immunoprecipitated by monoclonal antibodies from surface and metabolically labeled target cells. Once a family of individually distinct antigens has been defined and characterized, it will then be possible to explore their genetic origins and relationship to the distinct transplantation antigens of chemically induced sarcomas.